Water Releases Encourage Coho Salmon to Spawn

There’s been very little to report, until recently, on salmon spawning in Lagunitas Creek since my last update. December was the third driest on record, going back to 1849, and stream flows have been flat since the end of November. The long-range outlook is also bleak, with weather models predicting no rain for nearly two weeks. The lack of rain has prevented coho from getting up into the tributaries and some coho have been holding in a Lagunitas Creek pool for the last five weeks.

The situation improved this week when MMWD released a three-day “Upstream Migration Flow” from Kent Lake and increased stream flows from 20 cubic feet per second (CFS) to 35 CFS. These releases are required in mid-November and the beginning of December, January and February if rainfall during the previous month wasn’t adequate to provide a flow of a similar magnitude. The original goal was to provide enough depth for salmon to migrate upstream, although in the last 14 years we’ve seen very few fish migrate during these flows. We suspect that they’re reluctant to migrate in clear water because they would be vulnerable to predators, notably river otters. Coho are frequently seen migrating upstream under fairly low flows as long as the water is murky. No coho were observed during the previous upstream migration flow in mid-November.

Coho pair on a redd

So it was a very pleasant surprise to see coho migrating and spawning during this week’s upstream migration flow. MMWD biologists counted 20 new coho redds and 84 live coho in Lagunitas Creek, mostly upstream of Devil’s Gulch. Almost all of these fish were actively spawning and may not have had the fat reserves to wait much longer, murky water or not. To date we’ve seen 55 coho redds and 215 live coho. Some of these fish were likely counted over multiple weeks, so the actual number of fish may be closer to 150. Typically the coho spawning season is 80 percent complete by early January, although the peak of spawning has occurred later in a few years. Hopefully this is one of those years, when late rains arrive just in time to allow a lot more salmon to swim up into the tributaries and spawn.